Many multimedia systems are interfaced using High-Definition-Multimedia-Interface (HDMI), which provides an interface between any compatible digital audio/video source, such as a set-top box, DVD player, and A/V receiver and a compatible digital audio and/or video monitor, such as a digital television (DTV). Many prior art systems implement HDMI cable to interconnect these devices, e.g. the set-top box and Flat TV. The part that sends the Video/Audio data comprised in the set-top box is often referred to as source and the part that receives the data comprised in the A/V receiver (e.g. the TV) is often referred as the sink. Controlling the sink via the source, or vice verse, is done through the Consumer Electronics Control (CEC) channel, which is an option in the HDMI standard.
The power state of each individual device cannot be monitored in such prior art systems, only the power state of the whole system. Therefore, the power states can only partially be monitored, using the +5V and HPD mechanism. No distinction between ON and STB state is obtained, since in STB the +5V and HPD signal are still communicated.
In the newest/next generation of such multimedia systems where transmitter (TX) and receiver (RX) modules are required as intermediate objects to provide a connection between the source and the sink, where the modules are interfaced via HDMI, the power is much more complicated than in prior art systems. As an example, if the connection between the TX and RX is based on optical or wireless link, special precautions need to be taken since the link might not be transparent for all signals as available in the HDMI cable. Also, since the bandwidth required for the forward links for passing audio/video data from the source to the sink is much higher than the bandwidth required for the backward link from the sink to the source, the power behavior of the system becomes more complicated since the modules most likely have their own power states and may not have a complete transparent view on the peer device, as would be the case when a standard HDMI cable would be used. This puts some requirement on the TX and RX modules in order to implement a consistent power behavior. Also, the power state control via CEC command coupled to RC reception is not defined in any standard.